Field of the Invention
The present invention relates to a roller member being capable of conveying a sheet, a sheet feeding apparatus, and an image forming apparatus.
Description of the Related Art
In an image forming apparatus such as a copier and a printer including a sheet feeding apparatus feeding a sheet, a feed roller feeding the sheet is replaced as consumables by an operator such as a user and a service person, so that the feed roller is required to have high feeding performance and to be readily replaceable in the same time. Due to that, conventionally, there have been proposed sheet feeding apparatuses including various replacement mechanisms in order to improve replaceability of the feed roller.
Japanese Patent Application Laid-open No. 2002-104675 discloses a sheet feeding apparatus including such a replacement mechanism. That is, in the sheet feeding apparatus, a feed roller includes a roller base supported by a driving shaft, a substantially circular arc belt supporting member supported by the roller base, and an endless elastic belt member wrapped around the belt supporting member. According to this configuration, a part of the elastic belt member, exposed out of the belt supporting member, is configured to be a circular arc conveying portion rubbing and feeding a sheet, and a region other than the conveying portion of the elastic belt member is held on the roller base side.
This sheet feeding apparatus is configured such that the belt supporting member in a state of supporting the elastic belt member is assembled to the roller base while elastically deforming the region other than the conveying portion of the elastic belt member by pressing against the driving shaft. At this time, while the elastic belt member generates resilient force by being elastically deformed, the belt supporting member is fixed to the roller base by a lock portion (snap fit) by resisting against this resilient force. Therefore, if the lock portion is unlocked in removing the belt supporting member from the roller base due to maintenance or the like, the belt supporting member is detached from the roller base by the resilient force generated by the restoring elastic belt member.
Lately, downsizing of the feed roller and of the sheet feeding apparatus is required along with a demand on downsizing of the image forming apparatus. However, if the feed roller is downsized in the configuration described above, the conveying portion may be shortened. Therefore, it may become difficult to convey a sheet, by a single rotation of the feed roller, to a point where a tip of the sheet comes into contact with a drawing roller downstream in a sheet feeding direction.
Then, if the belt supporting member is configured so as to prolong a circular arc length thereof while keeping an outer circumferential length of the elastic belt member for the purpose of prolonging the conveying portion of the feed roller, an elastic deformation volume of the elastic belt member in attaching the elastic belt member to the belt supporting member may increase. Then, the resilient force in removing the belt supporting member from the roller base increases, and there is a possibility that the belt supporting member jumps out vigorously and falls down.
Still further, if the outer circumferential length of the belt is prolonged for the purpose of restraining the resilient force of the elastic belt member, there is a possibility that the elastic belt member is loosened and/or drops out of the belt supporting member after removing the belt supporting member out of the roller base, and consequently the replaceability of the elastic belt member may be hampered.